Abstract

An automatic voltage control technique, to optimise gas metal arc welding (GMAW) conditions for minimised fume generation, was compared to conventional constant-voltage operation on the influence of shielding gas on fume formation rate (FFR) and particle size distribution. Significant reductions in FFR were attributed to reductions in the arc length and current and to improved metal transfer stability, achieved by promoting the ‘drop-spray’ transfer condition and reducing repelled globular transfer. A general decrease in average particle size was observed when using the automatic control technique for the O2-bearing shielding gases, which is significant, as finer particulates are more likely to be inhaled into the lungs. The proposed mechanism to explain this behaviour was lower arc temperatures combined with an increase in the availability of oxygen, leading to nucleation of large amounts of extremely fine fume particles when the supercooling of the vapour was large. FFR increased as CO2 content increased due mainly to the dominant influence of CO2 on metal transfer and arc characteristics. It is recommended that the influence of shielding gas on FFR should be investigated using optimised welding conditions for each shielding gas composition for GMAW, especially when operating in the spray regime.

Supplementary material

Online resource 1Ar-5CO2-32 V video; long arc length with fluctuations in arc width. Droplets collided with one another and a few exploded due to arc interactions between colliding droplets. This appeared to generate increased fume. Larger droplets rotated within the arc. (AVI 3355 kb)

Online resource 5Ar-18CO2-32 V video; long arc length with fluctuations in width. Typically streaming spray transfer where the conglomeration of droplets was common. There were some exploding droplets due to arc interactions between droplets.) (AVI 3661 kb)

Online resource 8Ar-5CO2-2O2-32 V video; Very long arc length and fluctuations of arc width. Typically streaming spray transfer, where the conglomeration of droplets was common. There were several exploding droplets due to arc interactions between droplets (AVI 3524 kb)

Online resource 10Ar-5CO2-5O2-32 V video; long arc length with fluctuations in width. Typically streaming spray transfer where the conglomeration of droplets was common. Some large conglomerations were partially repelled by the arc below the droplet. There were only a few cases of exploding droplets due to arc interactions between droplets. (AVI 3617 kb)

Online resource 14Ar-18CO2-2O2-32 V video; Long arc length with streaming spray transfer. Substantial arc interactions were visible with larger conglomerated droplets, which appeared to generate increased fume. There were several instances of repelled globular transfer with short arc lengths and high fume generation (AVI 4431 kb)

Online resource 16Ar-20He-12CO2-32 V video; Mixture of spray transfer and repelled globular, where a long detachment event was observed at the end of the video. The brightness of the arc beneath the forming droplet, indicating a very hot arc, would generate increased fume. Larger droplets tend to rotate and cause arc instability. (AVI 3798 kb)

Online resource 19Ar-30He-6CO2-Auto video; Predominately repelled globular transfer with some arc instabilities. Very short arc length. There was a period of drop-spray transfer towards the end of the video. (AVI 4393 kb)

Online resource 21Ar-30He-10CO2-Auto video; Moderate arc length, similar to 32 V. Predominately streaming stray transfer, where there was significant narrowing of the end of the electrode. Arc interactions between streaming droplets is clearly visible. Arc more stable compared to the 32 V tests. (AVI 3555 kb)